A positive displacement pump typically utilizes a piston or diaphragm to act as a pumping member to move a liquid. The piston or diaphragm is reciprocated, and this tends to provide a pulsed output. The pulses or output surges can be reduced by using multiple chambers each with its own reciprocating member. However, typically the output from a positive displacement pump is not as even and continuous as may be desired for certain applications.
The pumping member or members can be reciprocated in various different ways. For example, in Hartley U.S. Pat. No. 4,797,069 a wobble plate is used in the drive train to drive multiple pistons in order to provide a multiple chamber pump. Although this pump works extremely well, it inherently provides a somewhat pulsed output.
In another prior art construction, a curved or wavy plate is rotated in a pumping chamber, with the curves of the plate providing the pumping action. This does reduce output surges. However, a separator slides back and forth in a slot to separate the liquid at inlet pressure from the liquid at outlet pressure, and it is difficult to seal the gap through which the separator moves. This wavy plate does not nutate and is of a rather complex configuration.
It is also known to rotate an inclined, flat plate in a pumping chamber. Although this is a simpler construction than the wavy plate, the inclined plate does not nutate and is subject to sealing problems.